1. Field of the Invention
This invention relates to hydrostatic float valves, particularly those useful with fluid feed systems for supplying fluid to the body cavity of a patient and particularly those that are capable of automatically shutting off the flow of said fluid when additional flow of said fluid would be dangerous to a patient, even though a manual control valve is inadvertently left open.
2. Description of the Technical Problem
A wide range of medications, nutrients and blood are commonly administered in fluid form to patients, animal as well as human. This is done by passing fluids containing a medication or nutrient or blood at a controlled rate via a needle or catheter into the body cavity of the patient, usually through a blood vessel, and preferably a vein. The flow rate at which such fluids are infused into the patient may be critical, depending on the medication or nutrient supplied and the state of health of the patient. Furthermore, it is also usually important to control the total volume of fluid infused.
For example, excessive and/or too rapidly applied doses of certain potent drugs used to counteract certain serious problems of patients may cause serious damage and even death to certain patients. For example, Lidocane, if applied in excessive doses to stop ventricular arrhythmias, will paralyze a patient's heart and cause cardiac arrest; an excessive dose of nitroglycerine to stop angina pain by relaxing the muscles of vascular walls may cause hypovolemic shock resulting in death, as do severe doses of nipride to reduce high blood pressure. Also, excessive doses of Dopomine, used to maintain adequate systemic blood pressure in patients suffering from shock, cause vascular systems to contract, blood pressure to increase and constrict blood vessels. With more potent drugs available today than previously, it becomes more and more important to control the flow rate within the range of five to sixty cubic centimeters per hour, the exact controlled flow rate being determined by the potency of drug used and the condition of the patient.
Prior to this invention, the rate of fluid flow for intravenous administration has been controlled manually, using a manually controlled drip chamber to control the rate at which drops fall through the drip chamber. This type of control is relatively simple as it needs only gravitational forces to maintain fluid flow through the drip chamber. However, manually controlled drip chambers are not satisfactory, because it is difficult to obtain flow rate that does not deviate appreciably from the desired flow rate, particularly when the fluids are administrated over an extended time or when it is necessary to replace an empty drip chamber with another drip chamber made to dimensions within sloppy tolerance compared to the dimensions of the replaced drip chamber or to replace a first fluid with a second fluid of different viscosity. Other factors that may cause loss of control of flow rate include change in fluid pressure and vibrational influences on the drip chamber. Furthermore, unless manual control valves of prior art systems are consciously closed, no other provision is made for stopping flow automatically in case of emergency.
In order to improve the accuracy of fluid flow rates, positive displacement infusion pumps have been used. While such pumps provide more accurately controlled flow rates than manual control that are independent of variations in fluid pressure and viscosity, such pumps operate with a manual control valve set wide open in conjunction with a fluid rate controller. Such an arrangement allows infusion of medication to occur in lethal doses whenever tubing, which feeds pumped fluid medications to an inserted catheter, is removed from the controller without first shutting off the manual control valve.